1. Field of the Invention
This invention relates to a system for correcting the steering force of a vehicle.
2. Description of the Related Art
It has been known in the art to correct the steering force of a vehicle. For example, Japanese Laid-Open Patent Application Hei 3(1991)-16879 discloses a system which estimates that the tire would slip on the road, when the detected yaw rate about the vehicle yaw axis is found to be beyond the value that must be generated by the steering behavior at that time, and drives the steering mechanism to generate the steering reaction force such that the steering behavior will correspond to that produced by the detected yaw rate.
Whether the yaw rate or some similar parameters such as the lateral gravity G (exerted laterally on the vehicle) is used as a parameter for monitoring, the prior art system is based on the concept of feedback control in which the steering angle manipulated by the vehicle driver is monitored as to whether the steering force is properly generated, and if not, the vehicle driver is suggested to correct steering. In general, the feedback control becomes effective after an error between the manipulated variable and controlled variable has occurred. Thus, the feedback control is useful as a symptomatic therapy, but is accordingly useless in avoiding the occurrence of an error beforehand.
Various sensors or detectors have been developed in recent years based on the advanced computer technology which can monitor the current vehicle running condition accurately. It therefore becomes possible to detect not only the parameter such as the lateral gravity G, but also it is possible to detect the deviation of the vehicle, through image processing, from the traffic lane on which the vehicle is traveling. It further becomes possible to monitor, by an ultrasonic sensor or a radar, as to whether another vehicle is closing in from behind on another lane. It has therefore been proposed in Japanese Laid-Open Patent Application Hei 4(1992)-19274 to predict a collision of vehicles if the driver changes the traffic lane to another.
The prior art system disclosed in the publication of 4-19274 is configured to do nothing more than simply decrease the amount of power-assist if the vehicle driver intends to steer the vehicle in a direction in which another vehicle exists. Specifically, the prior art system is unable to correct the steering force. More specifically, the prior art system is not configured to predict a future vehicle behavior or condition from the current vehicle running condition and to correct the steering force to a proper value such that the future vehicle behavior or condition will be equal to the behavior that the driver expects, or which provides information, as as the steering force, to the driver concerning the dangerousness which would otherwise occur based on a sign that the driver overlooked.
An object of the invention is to provide a system for correcting the steering force of a vehicle, which predicts a future vehicle behavior or condition from the current vehicle running condition and to correct the steering force to a proper value based on the concept of feedforward control such that the future vehicle behavior or condition will be equal to the behavior that the driver expects, and which provides information, in terms of steering, to the driver concerning the dangerousness which would otherwise occur based on a sign that the driver overlooked.
Moreover, there will be a situation in which, after having predicted a future vehicle condition or behavior, that to steer right, for example, may be safer than keeping the straight-ahead steering. If that is true, it will accordingly be favorable to provide the information to the driver by increasing the steering force (steering wheel torque or steering wheel actuating force) in the right direction or by decreasing that in the opposite direction.
Another object of the invention is therefore to provide a system for correcting the steering force of a vehicle, which predicts a future vehicle condition or behavior and based thereon, to provide the predicted information to the driver by making the steering force different in the right and left directions.
Furthermore, when, after having predicted a future vehicle condition or behavior, that to steer right, for example, may be safer than keeping the straight-ahead steering, it is favorable to positively invite the driver to steer right to avoid an accident, rather than simply suggesting it to him by decreasing the steering force in the right direction.
Yet another object of the invention is therefore to provide a system for correcting the steering force of a vehicle, which predicts a future vehicle condition or behavior and to positively invite the driver to carry out an accident avoiding operation, if needed.
Aside from the above, the invention is applicable not only to a vehicle equipped with power-assisted steering or power steering, but also to a vehicle equipped with muscular-energy steering. However, it is more advantageous if the system is applied to a vehicle equipped with power-assisted steering or power steering, since the system can be simpler and smaller in structure.
In the vehicle equipped with the power-assisted steering or power steering, it has been proposed to decrease the amount of power-assist to intensify the steering force (steering wheel actuating force or steering wheel torque). For example, it is known to increase the steering force by relieving pressurized oil supplied by a pump to an oil reservoir through a solenoid valve in the vehicle-speed-responsive-power-steering system. It is similarly known as taught in Japanese Patent Publication Sho 54(1979)-11171 to intensify the steering force by raising oil pressure in the reaction chamber. However, these prior art systems are configured to intensify the steering force in the right and left directions to an equal extent. Specifically, these prior art systems aim to prevent the occurrence of excessive steering than intended at a high vehicle speed.
In a vehicle equipped with the power-assisted steering or power steering, when it is estimated to be dangerous to, for example, steer right, it will accordingly be favorable to decrease the amount of power assist in the right direction so as to increase the steering force (steering wheel actuating force) in the same direction. On the other hand, when steering right is predicted to be safer, it will be favorable to increase the amount of power-assist in the right direction to decrease the steering force in the same direction. When configured thus, the driver will be invited or suggested to correct the steering in the right direction. Needless to say, it can be configured to apply a power as the steering force, independently of the driver's steering, to positively invite him to take an accident avoiding behavior.
A fourth object of the invention is therefore to provide a system for correcting the steering force of a vehicle equipped with power-assisted steering or power steering, which makes the steering force different in the right and left directions by increasing/decreasing the amount of power assist, or which causes the driver to take any accident avoiding behavior.
Even in the situations mentioned above, the driver must, of course, be free in steering the vehicle to run straight-ahead or turn left or right at his discretion. This is because the driver will not always overlook a curve or an obstacle ahead. Rather he might have an intention to divert from the road before the curve, or have a plan to stop before the obstacle or avoid it and then to stop.
A fifth object of the invention is therefore to provide a system for correcting the steering force of a vehicle, in which the driver can override the steering force corrected by the system, when the corrected steering force is inconsistent with his judgment.
Furthermore, there may be a situation in which, after having predicted a future vehicle condition or behavior, not to steer right or left would be better.
For example, there may be a situation in which other vehicles are about to pass or overtake in the right and left traffic lanes and in addition, there is found an obstacle ahead on the traffic lane on which the own vehicle is travelling. In this situation, it is favorable to increase or intensify the steering force in the right and left directions so as the to invite or suggest the driver to continue the straight-ahead driving or at least to keep the current traffic lane.
A sixth object of the invention is therefore to provide a system for correcting the steering force of a vehicle, which, when it is judged that to steer right or left is estimated to be not favorable, can increase or intensify the steering force in the right and left directions in response to the degree of judgement.
Moreover, in a vehicle equipped with the power-assist steering or power steering, if the steering force is only changed by increasing or decreasing the amount of power, the maximum steering force will theoretically be equal to that of the muscular-energy steering. In its minimum steering force, the road surface resistance will merely be decreased to zero such that the steering wheel can be moved by the driver's little finger. The system reliability will further be enhanced when, assuming that the driver is unable to steer the vehicle properly such as when dosing, it will be favorable to configure the system such that it recognizes the situation and operates to positively steer the vehicle.
With this respect, there has been proposed a system to automatically steer a vehicle which guides the vehicle to run along a desired travelling course. The automatically steered vehicle will be designed such that a human being (the driver) entrusts the system to steer during driving when a condition is satisfied. However, in the systems mentioned earlier there is not such a kind of automatic steering, because there has not been proposed an appropriate technique how to design it.
If a system can select an optimal traveling course in a traffic lane based on the detected current condition ahead of the vehicle, operate to steer the vehicle along the course and suggest to the driver how to steer in terms of steering force, the driver can recognize the direction to be steered by finding a direction with his hands in which the steering force is smaller and can steer the vehicle to easily run along the course. Such a kind of system acting as a good interface with a human being (the driver) has not been proposed.
In such a kind of system, if the system makes the steering force great such that the vehicle runs along a traffic lane, the vehicle can run along the course automatically even when the driver releases the steering wheel. Thus, by changing the degree of participation of the system in an analog manner, it becomes possible to continually alter the system from the state in which the vehicle is steered in cooperation with a human being to the state in which the vehicle is steered automatically. It becomes thus possible to design the system keeping pace with the development in the technology such as the environment recognition.
A seventh object of the invention is therefore to provide a system for correcting the steering force of a vehicle, which determines the amount of steering force optimal for causing the vehicle to run along a traffic lane when the driver is manipulating the steering wheel and provides information to him in terms of steering force such that he can easily steer the vehicle along the traffic lane, thereby making it possible for the system to coexist with a human being.
An eighth object of the invention is to provide a system for correcting the steering force of a vehicle, which can continually alter the degree of the human being's participation in vehicle steering, and although depending on the determination of control parameters, which will make it possible to realize automatic steering in which a human being does no longer participate in vehicle steering.
Furthermore, reviewing the aforesaid prior art (3-16879) carefully, it will easily be understood that the invention can not be realized on the mechanism disclosed there. The reason is that, since most of the power-assisted steering or power steering including that disclosed in the prior art reference adopts the so-called open center principle so as to save energy, the oil pressure for producing a bias force is not generated unless the steering wheel has been moved. In addition, although the rotary motion of steering generates the oil pressure and as a result, although it seems to be possible, at first view, to obtain the bias force as desired, we can not neglect the fact that the oil pressure varies with the reaction force from the road surface. Thus, the fact that the oil pressure to be generated is not constant makes the bias force unstable, requiring additional technique for stabilizing the oil pressure.
The prior art reference disclosed in its second embodiment, instead of the unstable hydraulic pressure, that electric force is used as an independent power-assist energy source. This will make it possible to determine the bias force with high accuracy.
However, the prior art system disclosed in the second embodiment has the following drawbacks.
(1) Since the mechanism for generating the bias force is housed in a rotating member, it is necessary to use slip rings which are poor in reliability. PA1 (2) Since the mechanisms for generating electromagnetic force is exposed in oil, the magnetic force attracts dust or rubbish in the oil, degrading the operation.
The prior art system thus leaves much to be improved.
A ninth object of the invention is therefore to provide a system for correcting the steering force of a vehicle, which is compact, easily manufactured and reliable in operation.
Apart from the above, it is preferable for the system to be urged to the neutral point (straight-ahead position) at the time of initiating the system.
A tenth object of the invention is to provide a system for correcting the steering force of a vehicle which can easily obtain the neutral point (straight-ahead position) at the time of initiating the system.